A2-A3 Digestive Organs

Relationship of digestive organs to pertitoneum

Peritoneum:

The peritoneum is a serous membrane in the abdominopelvic cavity. It has two layers:

• Parietal peritoneum: Lines the inside of the body wall.

• Visceral peritoneum: Covers the external surface of most digestive organs.

• Peritoneal cavity: The space between the two layers.

Mesentery:

A mesentery is the 2 layers of peritoneum fused back to back, it connects the body wall to the digestive system.

Its functions are to:

• Provide routes for blood vessels, lymphatics, and nerves to reach digestive organs/viscera.

• Hold organs in place.

• Store fat.

(some mesenteries are called omenta or ligaments)

Types of Mesentary

1. Dorsal mesentery

Most mesenteries are dorsal.

They attach the digestive organs to the posterior (back) abdominal wall.

2. Ventral mesentery

Attaches certain organs to the anterior (front) abdominal wall.

(Example: The mesentery that extends from the liver to the anterior abdominal wall.)

3. Retroperitoneal organs

During development, some organs become attached directly to the posterior abdominal wall.

As a result:

They lose their mesentery.

They end up behind the peritoneum.

Examples: pancreas, duodenum, large intestine

4. Intraperitoneal organs

These organs Keep their mesentery. Remain suspended within the peritoneal cavity.

Example: Stomach, jejunum, ileum

General Parts of the Stomach

Esophagus:

Extends from the pharynx to the stomach

Transports food and liquids from the throat to the stomach

Stomach

Function: acidic and mechanical digestion

Converts food into chyme

Small intestine

Extending from the pyloric sphincter to the ileocecal sphincter

3 subdivisions: duodenum, jejunum, & ileum

Function: digestion is completed and virtually all absorption occurs

Large intestine

Extends from the ileocecal valve to the anus

Subdivisions: cecum, appendix, colon, rectum, anal canal

Absorbs most of the remaining water, eliminates Indigestible food resides from the body

Parts of greater and lesser onemtum

Greater omentum

• Extends superiorly, laterally to the left, and inferiorly from the greater curvature of the stomach and the proximal part of the duodenum

-Gastrophrenic ligament: between the greater curvature of the stomach and the diaphragm

-Gastrosplenic ligament: between the greater curvature of the stomach and the spleen

-Gastrocolic ligament: from the inferior portion of the greater curvature of the stomach, descends anteriorly of the transverse colon and then ascending posteriorly, fusing with the visceral peritoneum of the transverse colon and the superior layer of its mesentery

Lesser omentum

• Connects the lesser curvature of the stomach and the proximal part of the duodenum to the liver

-Hepatogastric ligament

-Hepatoduodenal ligament

Peristalsis

Definition: Adjacent segments of the alimentary canal contract and relax alternating

Function: Moves food distally (forward) along the digestive tract.

Main purpose: Propulsion (pushing food forward), although some mixing may occur.

Bolus: A ball of chewed food mixed with saliva that moves through the esophagus.

Upper esophageal sphincter (UES): food enters forms pharynx to esophagus

Lower esophageal sphincter (LES): Relaxes for food entry to stomach and helps prevent stomach contents from flowing backward.

Curvature of Stomach

Cardia: surrounds the cardial orifice, the opening of the esophagus into the stomach

Fundus: dome-shaped part, tucked beneath the diaphragm

Body: the midportion of the stomach

Pylorus (Antrum & Canal): the distal part of the stomach; continues to the pyloric sphincter

Rugae: These longitudinal folds unfold to expands the stomach volume from 50ml to 4L

The stomach has two curvatures:

Greater curvature: the convex lateral surface of the stomach

Lesser curvature: the concave medial surface of the stomach

Small Intestine

• extending from the pyloric sphincter to the ileocecal valve (sphincter)

• the longest part of the alimentary canal

• Although 6-7m long in a cadaver, it is only 2-4 m long du ng life because of muscle tone

• about half the diameter of the large intestine (2.5-4cm)

Duodenum: the shortest intestinal subdivision; retroperitoneal

Jejunum: 2.5m long; intraperitoneal

Ileum: approximately 3.6m in length, intraperitoneal

Layers of Small Intestine

1. Superior part (1st part)

Receives chyme from the stomach through the pyloric sphincter.

2. Descending part (2nd part)

(Major Duodenal Papilla: small opening in the inner duodenum for entry of digestive juices (enzymes from pancreas & bile from gallbladder))

3. Horizontal part (3rd part)

Travels horizontally from right to left across the abdomen.

4. Ascending part (4th part)

Travels upward and joins the jejunum, the next part of the small intestine.

Parts of the Duodenum

1. Superior part (1st part)

Receives chyme from the stomach through the pyloric sphincter.

2. Descending part (2nd part)

(Major Duodenal Papilla: small opening in the inner duodenum for entry of digestive juices (enzymes from pancreas & bile from gallbladder))

3. Horizontal part (3rd part)

Travels horizontally from right to left across the abdomen.

4. Ascending part (4th part)

Travels upward and joins the jejunum, the next part of the small intestine.

Overview of large intestine

• Teniae coli: three thickened bands of longitudinal smooth muscle fibers

• Haustra: sacculations/pouches of the colon between the teniae coli

• Omental appendices: small and fatty appendices

• Semilunar folds: fold that help form the haustra

ileocecal valve: connects from ilieum to cecum

• Cecum: the first part of the large intestine, continues along ascending colon

• Appendix: The appendix is a small, closed-ended pouch attached to the back-inner side of the cecum, below, the small intestine connects to it.

• Ascending colon — travels upward on the right side.

• Right colic flexure (hepatic flexure) — the bend near the liver.

• Transverse colon — travels across the abdomen from right to left.

• Left colic flexure (splenic flexure) — the bend near the spleen.

• Descending colon — travels downward on the left side.

• Sigmoid colon — an S-shaped section that leads to the rectum.

Rectum and anal canal

1. Rectum

The final storage area for feces before it leaves the body.

2. Anal canal

• The last segment of the large intestine.

• Opens to the body exterior at the anus

3. Internal anal sphincter

Made of smooth muscle and works Involuntary

Relaxes during a bowel movement.

4. External anal sphincter

Made of skeletal muscle and works Voluntary

Helps you hold in feces until you are ready to have a bowel movement.